In a typical cellular radio system, mobile terminals (also known as mobile stations and mobile user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called “NodeB” or “B node”. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network providing wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP or “3G”) has undertaken to evolve further the predecessor technologies, e.g., GSM-based and/or second generation (“2G”) radio access network technologies.
Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected directly to a core network rather than to radio network controller (RNC) nodes. In LTE, in general, functions of a radio network controller (RNC) node are performed by the radio base stations nodes. As such, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes.
FIG. 1 illustrates a LTE system 10 sometimes referred to evolved-UTRAN (e-UTRAN). The LTE system includes Base Stations (BS) 13, 14 which communicate together over an X2 interface. The base stations 13, 14 are sometimes referred to as e-UTRAN node Bs (eNBs) in the 3GPP. The base stations 13, 14 communicate over an S1 interface with an evolved packet core (EPC) which includes one or more nodes labeled as mobility management entity (MME)/Serving Gateway (S-GW) 11. The MME handles the control plane (CP) in the EPC and S-GW handles the user plane (UP).
The base stations 13, 14 communicate over the radio/air interface with user equipments (UE) 12, a plurality of cells or sectors includes base stations that are geographically distributed in a known manner. The portion of the example system that is illustrated in FIG. 1 includes two cells A and B.
Mobility features of a mobile radio communications system can be divided into two areas: radio mobility, which mainly consists of handover involving UEs in active state which is also called RRC_CONNECTED state or EMM-CONNECTED state, and network mobility, which mainly consists of location management including location updates and paging involving UEs in idle state, which is also called RRC_IDLE state or EMM-IDLE state or just idle mode.
FIG. 2 illustrates two tracking areas TA1 and TA2. TA1 encompasses cells C1-C7 and tracking area TA2 encompasses representatives cells C8-C14. TA1 and TA2 cover a geographic area and might be owned or operated by the same operator or by two different operators, i.e. operator A operates TA1 and operator B operates TA2. Moving from one cell to another, network controlled handover is performed for UEs in active state and cell reselection is performed by UEs in idle state. The term “tracking area” used in LTE is equivalent to the term “location area” used in UTRAN.
In LTE active state, the UE position is known by the network at cell level or at least eNB level. When the UE transfers from idle to active state, area and access restriction information is sent from MME to the serving eNB 12 and it can be updated during active state. The area and access restriction information is valid for the concerned UE only, and hence each UE can have its unique area and access restriction information. The area and access restriction information is stored at the eNB in the UE context of the concerned UE and it is propagated from source eNB 13 to target eNB 14 at X2 handover or intra-MME/S-GW handover. At inter-MME/S-GW handover or at inter-RAT handover one or two MMEs are involved in the handover process and the EPC can then transfer new area and access restriction information to the target eNB. The area and access restriction information may include serving PLMN (Public Land Mobile Network) and Equivalent PLMNs as a list of allowed PLMNs, forbidden tracking areas and location areas, and forbidden inter-RATs (radio Access technology). This information is used in the eNB of cell A to determine whether a neighboring cell B is allowed for handover for the concerned UE.
In LTE idle state, the UE positions are known by the network at TA (tracking area) level. When camped on a cell, the UE searches regularly for a better cell according to the cell reselection criteria, which involves measurements of the serving and neighboring cells. The cell reselection criteria includes that the target cell has to be a suitable cell, which means that the PLMN, the tracking area and the location area may not be stored in the UE as forbidden PLMN, forbidden tracking area or forbidden location area, respectively. The cell reselection mechanism requires that each cell periodically broadcast the PLMN identity and the identity of its tracking area (or location area if UTRAN or GERAN cell). Each UE listens to the broadcast information on a cell's broadcast channel and stores the current PLMN identity and tracking area identity. If the received tracking area identity differs from the one stored by the UE, a tracking area update procedure is triggered by the UE. The MME can reject a tracking area update for many causes; one example is so called forbidden tracking area which indicates that the received tracking area is forbidden for the UE to camp on. When the UE receives this rejection cause, it stores the broadcasted tracking area identity as forbidden tracking area, and the UE start to search for another cell. Similarly the MME can reject a tracking area update with cause forbidden PLMN at which the UE stores the broadcasted PLMN identity as forbidden, and the UE start to search for a network with another PLMN identity.
In conclusion, it is possible to perform mobility restriction of a UE in both active state and idle state on PLMN identity, tracking area and location area. At active state in LTE it is also possible to perform handover restriction on one or several radio access technologies, by setting forbidden inter-RAT. For a UE with the forbidden inter-RAT set to UTRAN, the handover is forbidden to all UTRAN neighbor cells, independently of what PLMN identities or location areas the UTRAN cells belong to. It is another way to say that all location areas in UTRAN are forbidden or another way to say that the PLMN identity of the UTRAN is not allowed.
The forbidden inter-RAT is more than this, since it does not require that location areas are different in UTRAN and GSM EDGE Radio Access Network (GERAN) or that PLMN identity of the UTRAN is not used in any other radio access technology to enable that only UTRAN is forbidden. However, since no forbidden inter-RAT concept exists for UEs in idle state, the location areas or PLMN has to be different in different RATs to enable the same area and access restriction for a UE in idle state as in active state.
A problem with the forbidden inter-RAT is that the operator might not want to block all carrier frequencies on an Inter-RAT. For example, when two operators, operator A and operator B, share the same LTE network and operator A have signed a roaming agreement to allow subscribers of operator B to roam in for example GSM 900 only, but there are GSM 1800 cells in the GERAN network of operator A as well that operator A wants to block. Another example could be that a service level agreement is signed with a virtual operator to allow access of the virtual operators subscribers in LTE and UMTS 2100 but not in UMTS 900, which is also available in the same PLMN and which can not be blocked by forbidden inter-RAT in the area and access restriction information. Moreover, the UMTS network could consist of hierarchical cell structures, and the subscriber of the virtual operator could be allowed access only to the macro cells in that UMTS network.
Another problem with the area and access restriction information is that an operator might want to block a certain LTE carrier frequency and there is no simple way to perform this. For example, some operators offer a special home base station access where all customers that have home base station from that operator are offered access to all other home base station within the operator's network. Customers that do not have any home base station would not be allowed access to any home base stations in the network; instead they would have the frequency of the home base stations as forbidden frequency. This assumes that a special carrier frequency is used for the home base stations only.
Yet another problem with the area and access restriction information is that an operator only wants to perform access restriction on an individual location area of one frequency, i.e. there is a location area 1 using frequency 1 and 2 but only frequency 2 in area 1 should be restricted for some subscribers. This would mean that an operator do not want to restrict frequency 2 everywhere in the network, but only when some subscribers are in area 1 of frequency 1. Hence, the operator would like to change the forbidden frequency list when moving in and out of area 1. The area could be tracking area, location area, service area or maybe some new area concept that does not exist currently in 3GPP standard.
One way to perform area and access restrictions to a carrier frequency or set of frequencies in LTE or in inter-RAT would be to use unique tracking areas (for LTE frequencies) and/or unique location areas (for inter-RAT frequencies) in each frequency to which some users should be blocked. In this case there is no need to send any restriction information for UEs that should be allowed to access all frequencies. The MME sends Serving PLMN and a list of forbidden tracking areas for users that should be blocked from accessing some frequencies. The list of forbidden tracking areas and/or location areas should contain those identities that are used for the carrier frequencies that are not allowed for access. If not all identities of the un-allowed carriers frequencies can be listed then the list should contain the identities used in the surrounding area, primarily. This has the disadvantages that there will be tracking area updates when changing frequency within the RAT for allowed users. It also has the disadvantage that the restriction information will be long and probably needs to be updated during mobility over tracking areas. Since the restriction information list will be long it will also require significant configuration of restriction information in the core network. The MME needs to have neighbor relation information about the tracking and/or location areas, i.e. geographical information of the tracking areas and location areas. If the location areas between UTRAN frequencies or between GERAN frequencies or even between UTRAN and GERAN are configured with same location area identities then a cumbersome reconfiguration of the network would be necessary. Reconfiguring location areas will have a negative effect of serviceability of a network in operation.